Prosthetic device including electrostatically spun fibrous layer and method for making the same

ABSTRACT

In accordance with certain embodiments of the present disclosure, a process of forming a prosthetic device is provided. The process includes forming a dispersion of polymeric nanofibers, a fiberizing polymer, and a solvent, the dispersion having a viscosity of at least about 50,000 cPs. A tubular frame is positioned over a tubular polymeric structure. Nanofibers from the dispersion are electrospun onto the tubular frame to form a prosthetic device. The prosthetic device is heated.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. application Ser. No. 13/564,927, filed on Aug. 2, 2012; which application is a continuation application of U.S. application Ser. No. 12/852,993, filed on Aug. 9, 2010; now U.S. Pat. No. 8,262,979, issued Sep. 11, 2012; which is based on and claims priority to U.S. Provisional Application 61/232,252, filed Aug. 7, 2009, which are incorporated by reference herein.

BACKGROUND

The successful use of extruded tubes of expanded polytetrafluoroethylene (ePTFE) as a synthetic implantable vascular prostheses or tubular graft, designed in particular for the application of synthetic vascular prosthesis or tubular grafts is well known and documented. ePTFE, validated through significant clinical studies, is particularly suitable as a vascular prosthesis or tubular graft as it exhibits superior bio-compatibility and can be mechanically manipulated to form a well defined porous microstructure known to promote endothelialization. PTFE has proven to exhibit a low thrombogenic response in vascular applications. When seeded or infused with a cardio protective agent, the microporous structure, formed of nodes and fibrils, allows natural tissue ingrowth and cell endothelialization when implanted in the vascular system. This contributes to long term healing and patency of the tubular graft.

In the prior art, U.S. Pat. No. 6,436,135 Goldfarb, the microstructure of a synthetic vascular prostheses or tubular graft formed of ePTFE is categorized by a fibrous state which is further defined by irregularly spaced nodes interconnected by elongated fibrils or microfibers. The method and techniques for creating this structure have been known for more than three decades and is, in fact, quite simple to one skilled in the art. The distance between the node surfaces that is spanned by the fibrils is defined as the inter-nodal distance (IND). A tubular graft having a specific range of IND enhances tissue ingrowth and cell endothelialization as the tubular graft is inherently porous. The IND range is also small enough to prevent transmural blood flow and thrombosis but not less than the maximum dimension of the average red blood cell, between 6μ and 80μ.

The prior art is filled with examples of microporous ePTFE tubular vascular prosthesis or tubular grafts. The porosity of an ePTFE vascular prosthesis or tubular graft is controlled by the mechanical formation of the IND or the microporous structure of the tube. IND with the defined structure referenced produces results of tissue ingrowth as well as cell endothelialization along the inner and outer surface of the vascular prosthesis or tubular graft.

Similarly, stents are commonly used to restore and maintain body passages, such as blood vessels. Often, biocompatible materials, including grafts, can be provided on the inner or outer surfaces of the stent to reduce reactions associated with contact of the stent with the body.

However, it is difficult with such conventional devices to manipulate mechanical properties, cellular proliferation, cellular permeability, fluid permeability, adhesion to a structural frame, and/or incorporation of an active therapeutic component in the same. Further, such conventional devices do not allow for coating of complex geometries that otherwise could not be covered with ePTFE or other materials alone.

Thus, a need exists for processes that address the deficiencies described above. Prosthetic devices made from such processes would also be particularly beneficial.

SUMMARY

In accordance with certain embodiments of the present disclosure, a process of forming a prosthetic device is provided. The process includes forming a dispersion of polymeric nanofibers, a fiberizing polymer, and a solvent, the dispersion having a viscosity of at least about 50,000 cPs. A tubular frame, such as a stent, is positioned over a tubular polymeric structure. Nanofibers from the dispersion are electrospun onto the tubular frame to form a prosthetic device. The prosthetic device is heated.

In other embodiments of the present disclosure, a process for forming a prosthetic device includes forming a dispersion of polymeric nanofibers, a fiberizing polymer, and a solvent, the dispersion having a viscosity of at least about 50,000 cPs. Nanofibers from the dispersion are electrospun onto a tubular polymeric structure. A layer of polymeric material is wrapped over the nanofibers and around the tubular polymeric structure to form a prosthetic device. The composite structure is heated.

In still other embodiments of the present disclosure, a process of forming a prosthetic device is disclosed. The process includes forming a dispersion of polymeric nanofibers, a fiberizing polymer, and a solvent, the dispersion having a viscosity of at least about 50,000 cPs. A tubular frame is positioned over a tubular polymeric structure. Nanofibers from the dispersion are electrospun onto the tubular frame. A layer of polymeric material is wrapped over the nanofibers and around the tubular frame and tubular polymeric structure to form a prosthetic device. The prosthetic device is heated.

Other features and aspects of the present disclosure are discussed in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure, including the best mode thereof, directed to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, which makes reference to the appended figures in which:

FIGS. 1-4 illustrate cross-sectional views of different prosthetic devices in accordance with the present disclosure.

DETAILED DESCRIPTION

Reference now will be made in detail to various embodiments of the disclosure, one or more examples of which are set forth below. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. For instance, features illustrated or described as part of one embodiment, can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents.

The present invention is related to tubular prosthetic devices (also referred to herein as “tubular vascular prostheses” and/or “tubular grafts” and/or “tubular frames”) comprising electrospun (also referred to herein as “espin” and/or “espun” and/or “espinning”) fibers around a central lumen of such devices. In certain embodiments, the central lumen can include expanded polytetrafluoroethylene (also referred to herein as “ePTFE”). In certain embodiments, the espin fibers can include polytetrafluoroethylene (also referred to herein as “espin PTFE”), however, many other suitable materials can be espun and used in addition to or in combination with such espin PTFE. For example, other suitable materials that can be espun in accordance with the present disclosure include nylons, polyurethanes (PU), polyesters, fluorinated ethylene propylene (FEP), or the like. Polymers that can be placed in a solution have the potential to be espun. Polymer particles that can be made into dispersions (such as, PTFE, FEP, and the like) also have the potential to be espun. The dispersions (espun PTFE) must be sintered to develop the desired properties, but many polymers espun from solution develop their properties during spinning and drying. The attachment of the espin layer(s) can occur during sintering.

In certain embodiments of the present disclosure, an implantable microporous tubular vascular prosthesis or tubular graft comprised primarily of micron and sub-micron sized electrostatically spun PTFE fibers in a random orientation around a central lumen is described. The tubular vascular prosthesis or tubular graft may include one or more layers forming a composite structure of electrostatically spun PTFE fibers around a tubular structure such as a tubular vascular prosthesis, tubular graft, tubular frame, or combinations thereof.

The present disclosure offers a number of advantages over conventional processes and devices including: 1) the ability to incorporate layers with vastly different pore structures and sizes, these different structural layers can be used to manipulate mechanical properties, cellular proliferation, cellular permeability, fluid permeability, adhesion to a structural frame, and/or incorporation of an active therapeutic component; 2) the ability to make a composite construction with vastly different components enabling a broader range of therapeutic uses and structures; 3) improved bonding of PTFE layers to structural frames and to other layers of the construct; 4) the ability to incorporate an espin layer that closely mimics that of the extracellular matrix affording greater control of cellular response; and 5) enabling the coating of complex geometries that otherwise could not be covered with ePTFE or other materials alone.

The tubular structure can include a self sealing thermoplastic or elastomeric component, as described above, as well as a selection of bioactive agents. Examples of such bioactive agents that can be utilized in connection with the devices of the present disclosure include but are not limited to antibiotics, antifungals and antivirals such as erythromycin, tetracycline, aminoglycosides, cephalosporins, quinolones, penicillins, sulfonamides, ketoconazole, miconazole, acyclovir, ganciclovir, azidothymidine, vitamins, interferon; anticonvulsants such as phenytoin and valproic acid; antidepressants such as amitriptyline and trazodone; antiparkinsonism drugs; cardiovascular agents such as calcium channel blockers, antiarythmics, beta blockers; antineoplastics such as cisplatin and methotrexate, corticosteroids such as dexamethasone, hydrocortisone, prednisolone, and triamcinolone; NSAIDs such as ibuprofen, salicylates indomethacin, piroxicam; hormones such as progesterone, estrogen, testosterone; growth factors; carbonic anhydrase inhibitors such as acetazolamide; prostaglandins; antiangiogenic agents; neuroprotectants; neurotrophins; growth factors; cytokines; chemokines; cells such as stem cells, primary cells, and genetically engineered cells; tissues; and other agents known to those skilled in the art.

Referring to FIG. 1, a cross-section view of a structure in accordance with the present disclosure is illustrated. The structure includes an ePTFE layer 1 and an espin layer 2. Such a configuration may be processed as a component to be used in the construction of a graft or stent-graft assembly depending on the geometrical shape and properties desired. It may also be used as a covering for other medical devices including but not limited to occlusion devices, defect closure devices, cellular encapsulation devices, regenerative medicine scaffolds, cosmetic implants, cardiovascular patches and abdominal patches as examples. However, this list is not all inclusive and many other applications are contemplated in accordance with the present disclosure.

The inner (blood contacting) and outer (tissue contacting) layers of the present disclosure may have different porosities to enhance or inhibit, respectively, cellular ingrowth or attachment. Applications for the implantable electrostatically spun vascular prosthesis would include but not be limited to artificial by-pass graft, coronary artery by-pass graft, by-pass shunt, hemodialysis, arteriovenous graft, homograft, pulmonary allograft, or pulmonary shunt. This tubular structure can include characteristics of enhanced radial tensile strength, suture hole tearing resistance and enhanced axial tear resistance.

Referring to FIG. 2, a cross-section view of a device in accordance with the present disclosure is illustrated. The device includes an ePTFE layer 1, a frame 3 (such as a stent frame), and an espin layer 2. Such a configuration may be used in an application where it is desirable to bond ePTFE to a formed structure such as a stent, occlusion device or other frame. The espin layer provides adhesion while also providing a substantially different pore size and structure on the luminal or abluminal surface depending on the application. In such a configuration, the espin layer can be applied directly to the surface of the frame or added as a preformed sheet that is combined with the ePTFE and frame as part of the sintering or curing process. In general, such a configuration could be utilized in any application where the encapsulation of a support frame is desirable. For instance, such a configuration could be used in connection with a conventional stent.

Various stent types and stent constructions may be employed in the present disclosure. Among the various stents useful include, without limitation, self-expanding stents and balloon expandable extents. The stents may be capable of radially contracting, as well. Self-expanding stents include those that have a spring-like action which causes the stent to radially expand, or stents which expand due to the memory properties of the stent material for a particular configuration at a certain temperature. Nitinol is one material which has the ability to perform well while both in spring-like mode, as well as in a memory mode based on temperature. Other materials contemplated by the present disclosure include, but are not limited to, stainless steel, platinum, gold, titanium and other biocompatible metals, as well as polymeric stents.

The configuration of the stent may also be chosen from any suitable geometry as would be known in the art. For example, wire stents can be fastened into a continuous helical pattern, with or without a wave-like or zig-zag in the wire, to form a radially deformable stent. Individual rings or circular members can be linked together such as by struts, sutures, welding or interlacing or locking of the rings to form a tubular stent. Tubular stents useful in the present invention also include those formed by etching or cutting a pattern from a tube. Such stents are often referred to as slotted stents. Furthermore, stents may be formed by etching a pattern into a material or mold and depositing stent material in the pattern, such as by chemical vapor deposition or the like.

Turning to FIG. 3, a cross-section view of another configuration is illustrated. The configuration includes an ePTFE layer 1, an espin layer 2, and another ePTFE layer 1, such that the espin layer 2 is sandwiched between the ePTFE layers 1. Such a construction allows the user to manipulate the mechanical properties of the composite as desired, for example improving material recovery after compression. The espin material selection can be adjusted to improve bonding properties between layers and the espin layer can be used to inhibit cellular proliferation through the middle on the construction. In this instance, it may be advantageous to allow cells to migrate and proliferate from both sides (luminal and abluminal in the case of a graft) but communication between the two may not be desired. The middle espin layer can be designed with a porosity that will inhibit this cellular communication.

Turning to FIG. 4, a cross-section of yet another configuration in accordance with the present disclosure is illustrated. The device includes an ePTFE layer 1, an espin layer 2, a frame 3, and another ePTFE layer 1. In this manner, the frame increases the radial strength of the overall construction and also promotes recovery during deployment of the construction. For instance, in certain embodiments of the present disclosure, the frame is a stent. The stent frame provides a structural backbone within the structure, which prevents suture wall tear out.

The electro-spun layer is preferably applied directly to the frame through electrospinning methods understood by those skilled in the art; however, it could also be applied by lamination as well. The technique involves pressing an espun layer onto a second material layer and heating to a complimentary temperature. In all configurations, the design can include or exclude a structural frame. These frames can take the form of stents, occlusion coils or frames, regenerative medicine scaffolds, structural reinforcements, pacing or monitoring leads, tissue anchors or tacks, biological stimulation devices, biomimetic implants, signal receivers or transmitters, orthopedic fixation devices or any other metallic, polymeric, ceramic or other therapeutic device.

The properties and characteristics of the composite material are a compilation of the frame, espun, and ePTFE membrane layers. The composite can be prepared with controlled fiber, node, and fibril sizes and manipulated mechanically, such as to improve bond strength, elongation properties, and tensile strengths, in the final composite.

Typical construction of multiple layers may produce thickness ranging from about 0.0001 inches to about 0.25 inches overall thicknesses at widths of about 0.032 inches to about 80 inches. The individual layers can have a thickness that varies from about 0.0001 inches to about 0.25 inches. Final material size varies greatly as the composites can be produced as sheets or tubes at continuous roll lengths. The composite internodal distance (IND) can be about 0.1 to about 200 μm with porosity ranging from about 20 to 90%. Pore structure as defined by ASTM F316, incorporated by reference herein, can range from about 0.05 to about 50 μm. Due to the construction of the composites, the IND, pore size and porosity can vary from layer to layer, within the cross section of the composite, depending on the construction. An example would be an asymmetrical construction where pores change in size from large to small based on layer evaluations from surface to surface throughout the media.

The materials used in the construction of frame and graft structures as described herein, may be produced as an assembly using prefabricated components, from materials described herein. The materials may be assembled in individual layers or in bi-layers. It may be beneficial to produce a construction as illustrated in FIG. 2 as a component, to be used in another construction described herein. For the embodiment illustrated in FIG. 4, prefabricated components can be coupled with the final frame and additional layers of ePTFE as desired to produce the finalized assembly.

For instance, in embodiments in which the electrospun layer is part of a tubular structure, as previously described herein, the diameter of fibers in the espin layer can range from about 10 nm to 2000 nm in size, wall thicknesses ranging from about 75μ to 1.5 mm, and average inside diameter ranging from about 0.2 mm to 50 mm.

The devices of the present disclosure can be prepared with controlled fiber, node and fibril sizes and manipulated mechanical values such as bond strength, elongation properties and tensile strengths.

Expanded PTFE is comprised of a microstructure consisting of solid nodes interconnected by fine, highly oriented fibrils. The expanded PTFE nodes and fibrils provide unique biocompatible porous structures. The microstructure of the material can be adjusted to provide a matrix for cellular attachment and in-growth. The expanded PTFE and electrospun PTFE microstructures are designed to enhance, inhibit or retard the migration of endothelium during the early phase of healing.

As an example, an ePTFE microstructures which have a node to fibril distance of about 10˜20 μm permit very little transmural cellular in-growth. Optimal porosity for cellular in growth ranges between 20 and 80 μm. Studies have shown porosity of >120 μm have been associated with reduced in growth and poor Neointima adhesion based on the smaller surface are available for cellular adhesion and locomotion.

In certain embodiments of the present disclosure, the process can require a dispersion or suspension of PTFE solids between about 10 to 85% by weight to aid in the processing of the collected fibrous mat into a form that has sufficient green strength. However, as described above, other suitable polymers can be utilized for the espin dispersion. If the solid content in the dispersion is too low, there will be no, or poor, mechanical integrity to the resulting material. Second, the selection of the polymer used to increase the viscosity of the solution, suspension or dispersion to be spun must be selected carefully.

Additionally, when sintering or bonding espin layers it is necessary to insure that temperatures are selected to properly sinter the material, such that the resulting product has good mechanical integrity.

To produce a non-woven espin PTFE material, a narrow particle size distribution PTFE powder is provided in an aqueous dispersion. The particle size would preferably be about 0.05 to 0.8μ. About 1 to 10 wt % by weight of a fiberizing polymer is added to the volume of PTFE aqueous dispersion. The fiberizing polymer should have a high solubility in water with a solubility of greater than about 0.5 wt % being preferred. It is preferable that the fiberizing polymer has an ash content of less than about 5 wt %, when sintered at about 400° C., with even lower being more preferred. Without limit thereto, particularly preferred fiberizing polymers can include dextran, alginates, chitosan, guar gum compounds, starch, polyvinylpyridine compounds, cellulosic compounds, cellulose ether, hydrolyzed polyacrylamides, polyacrylates, polycarboxylates, polyvinyl alcohol, polyethylene oxide, polyethylene glycol, polyethylene imine, polyvinylpyrrolodone, polylactic acid, polymethacrylic acid polyitaconic acid, poly 2-hydoxyelthyl acrylate, poly 2-dimethylaminoethyl methacrylate-co-acrylamide, poly n-isopropylacrylamde, poly 2-acrylamido-2-methyl-1-propanesulfonic acid, poly(methoxyethylene), poly(vinyl alcohol), poly(vinyl alcohol) 12% acetyl, poly(2,4-dimethyl-6-triazinylethylene), poly(3-morpholinylethylene), poly(N-1,2,4-triazolyethylene), poly(vinyl sulfoxide), poly(vinyl amine), poly(N-vinyl pyrrolidone-co-vinyl acetate), poly(g-glutamic acid), poly(N-propanoyliminoethylene), poly(4-amino-sulfo-aniline), poly[N-(p-sulphophenyl)amino-3-hydroxymethyl-1,4-phenyleneimino-1,4-phenylene)], isopropyl cellulose, hydroxyethyl, hydroxylpropyl cellulose, cellulose acetate, cellulose nitrate, alginic ammonium salts, i-carrageenan, N-[(3′-hydroxy-2′,3′-dicarboxy)ethyl]chitosan, konjac glocomannan, pullulan, xanthan gum, poly(allyammonium chloride), poly(allyammonium phosphate), poly(diallydimethylammonium chloride), poly(benzyltrimethylammonium chloride), poly(dimethyldodecyl(2-acrylamidoethyly) ammonium bromide), poly(4-N-butylpyridiniumethylene iodine), poly(2-N-methylpridiniummethylene iodine), poly(N methylpryidinium-2,5-diylethenylene), polyethylene glycol polymers and copolymers, cellulose ethyl ether, cellulose ethyl hydroxyethyl ether, cellulose methyl hydroxyethyl ether, poly(l-glycerol methacrylate), poly(2-ethyl-2-oxazoline), poly(2-hydroxyethyl methacrylate/methacrylic acid) 90:10, poly(2-hydroxypropyl methacrylate), poly(2-methacryloxyethyltrimethylammonium bromide), poly(2-vinyl-1-methylpyridinium bromide), poly(2-vinylpyridine N-oxide), poly(2-vinylpyridine), poly(3-chloro-2-hydroxypropyl-2-methacryloxyethyldimethylammonium chloride), poly(4-vinylpyridine N-oxide), poly(4-vinylpyridine), poly(acrylamide/2-methacryloxyethyltrimethylammonium bromide) 80:20, poly(acrylamide/acrylic acid), poly(allylamine hydrochloride), poly(butadiene/maleic acid), poly(diallyldimethylammonium chloride), poly(ethyl acrylate/acrylic acid), poly(ethylene glycol) bis (2-aminoethyl), poly(ethylene glycol) monomethyl ether, poly(ethylene glycol)-bisphenol A diglycidyl ether adduct, poly(ethylene oxide-b-propylene oxide), poly(ethylene/acrylic acid) 92:8, poly(1-lysine hydrobromide), poly(l-lysine hydrobromide), poly(maleic acid), poly(n-butyl acrylate/2-methacryloxyethyltrimethylammonium bromide), poly(N-iso-propylacrylamide), poly(N-vinylpyrrolidone/2-dimethylaminoethyl methacrylate), dimethyl sulfatequaternary, poly(N-vinylpyrrolidone/vinyl acetate), poly(oxyethylene) sorbitan monolaurate (Tween 20®), poly(styrenesulfonic acid), poly(vinyl alcohol), N-methyl-4(4′-formylstyryl)pyridinium, methosulfate acetal, poly(vinyl methyl ether), poly(vinylamine) hydrochloride, poly(vinylphosphonic acid), poly(vinylsulfonic acid) sodium salt, polyaniline, and combinations thereof. Again, however, such fiberizing polymers are also contemplated for use with other polymer espin dispersions.

A particularly preferred fiberizing polymer is polyethylene oxide with a molecular weight between about 50,000 to 4,000,000 amu polyethyleneoxide. After mixing, the PTFE and fiberizing polymer dispersion is preferably allowed to homogenize. In a particularly preferred method the polymer solution is allowed to form slowly, without agitation, followed by transfer to a jar roller that will turn it at a constant rate for several more days. The present disclosure contemplates the use of dispersions of greater than 50,000 cPs to provide for more uniform and consistent fiber formation as well as faster builds. It is preferred to create a uniform solution that has little to no air trapped in the resulting highly viscous mixture. Once the dispersion is of uniform consistency it is preferably filtered to remove any clumps or gels. The filtered dispersion with the desired viscosity is then loaded, in a controlled pumping device with a fixed conductive element which acts as the charge source.

A particularly preferred conductive element is one with one or several orifices. The orifice size is preferably, but not limited to, about 0.01 to 3.0 mm in diameter. The ejection volume from the pumping device is set to a predetermined rate that is dependent on the form being made and the desired fiber diameters. The charge source is preferably connected to the positive side of a precision DC power supply. The negative side of the power supply is preferably connected to the collection surface or target. The polarity can be reversed but this is not preferred.

The surface can be a drum, device or sheet. The surface can be a metal, ceramic or polymeric material with particularly preferred materials selected from stainless steel, cobalt chrome, nickel titanium (nitinol) and magnesium alloys. The voltage on the power supply is increased to the desired voltage to uniformly draw out the polymer/PTFE solution.

The applied voltage is typically from about 2,000 to 80,000 volts. The charge induced by the connection of the power supply repels the charged polymer away from the charge source and attracts them to the collection surface.

The collection target is preferably placed perpendicular to the pump and orifice system and is moved in at least one direction such that the entire surface is uniformly covered, with the fibers drawn towards the target. Once the collection surface has been adequately covered the material is preferably cured, sintered, and dried (which can occur simultaneously or in a series of steps), either in place, by placing the entire collection surface in an oven, or by removing the sheet tube or other form from the collection surface and sintering it in an oven.

It is well known to those skilled in the art that espin fabrics undergo shrinkage upon sintering. While not limited to any theory the shrinkage is believe to occur in two steps. Initially, the fibers and fabrics as spun contain both water and a fiberizing polymer as previously described. Upon completion of spinning the samples dry and undergo a small degree of fiber rearrangement. At a later time the samples are heated by exposing the fibers and fabrics to temperatures of about 35° C. to about 485° C. for a period of time.

To accommodate for shrinkage, the fiber and fabrics can be spun onto an expanded structure. The structure can then be removed or contracted. During sintering of the espin layer, the fabric shrinks to a smaller size without cracking. Another method involves spinning the fibers and fabrics onto a structure which can then be expanded and/or contracted prior to or during sintering. The range of contraction or expansion and contraction is on the order of about 3 to 100% and depends upon the thickness and size of the electrodeposited fabric. Alternatively the espin layer can be placed upon a surface which also contracts during sintering.

For a sheet of fabric, if the direction of the deposition is given as the perpendicular to the plane of the fabric then contraction or expansion/contraction must occur in at least one or more of the directions in the plane of the fabric. For a fabric deposited upon a cylindrical surface the fabric must be contracted or contracted/expanded radially and/or longitudinally. For a spherical surface the fabric must be contracted or contracted/expanded radially. These basic concepts of contraction and/or expansion/contraction can be applied to any electrospun fabric independent to the shape of the surface upon which it was spun. Thus, very complex fabric shapes based upon espin fabric become possible.

The espin layer is preferably fibrous. Particularly preferred espin fibers have a diameter of at least 0.1μ. In a particularly preferred embodiment the product, after sintering, has fibers deposited in a density such there is a range of distances of 0.1 to 50μ between points of contact.

The present disclosure can be better understood with reference to the following examples.

EXAMPLES

The following general guidelines are used for the processing examples described herein of various ePTFE and espin composite constructions.

1. In espin PTFE embodiments, the viscosity of the dispersion may be changed by the addition or removal of water from the dispersion without changing the PEO to PTFE ratio.

2. A radially expanded ePTFE tube or biaxial oriented sheet is placed over a round or flat base plate to form a desired geometric shape.

3. The espin polymer layer is applied at a desired thickness, typically about 0.5 to 1000 μm, onto the ePTFE or onto a surface which is then mated to the ePTFE membrane, resulting in a composite structure.

4. If the espin coating is applied wet to the ePTFE, it is allowed to dry before moving to the next process. However, if it is processed as a single espin sheet and has dried, it will be mated to the oriented porous ePTFE layer. The mating process between the materials can be repeated multiple times until a desired multilayered composite structure is created.

5. The ePTFE/espin composite is then covered with a non-sticking release foil. 6. Once the composite is positioned against a base tool, pressure is applied to the surface of the foil, thereby aiding the bonding process.

7. The composite construction is placed in an oven at temperatures of about 35° C. to about 485° C. to allow all materials to bond together. The bonding temperature selection is based on material selection.

8. Once the part is removed from the oven and cooled at a rate of about 15 to 25 degrees per minute, it is uncovered and tested for specified properties.

Example 1 Type I Construction: ePTFE/espun PTFE

A biaxially (Biax) expanded approximately 10 cm long ePTFE tube with an intermodal distance (IND) of 20μ, internal diameter (ID) of 4 mm, wall thickness (WT) of 0.1 mm, and porosity of 77.27% was placed over and centered along a 4 mm exterior diameter (OD) stainless steel (SS) tube of 35 cm length. The tube assembly was placed into a rotating chuck such that it was positioned to allow espinning along the entire length of the turning tube assembly.

An approximately 85,900 cPs espinning dispersion based on a mixture of 4.2% (PEO/PTFE), 300,000 amu polyethylene oxide and Daikin D210 60% PTFE dispersion which had been allowed to homogenize and then turned and filtered to achieve a smooth consistency was placed into a 10 ml plastic syringe fitted with a 22 gauge needle. The syringe was placed into a Harvard Model 702100 syringe pump and set to 2.0 ml/hour pumping rate. The needle tip was positioned at approximately 9.5 cm from the rotating tube assembly. The rotation of the tube assembly was approximately 60 rpm. A traverse was used to move the espinning needle along the length of the tube with a rate of travel of 3.2 mm/sec. The return points for the traverse were set at the ends of the Biax tube. A voltage of 9.2 kV was employed. PTFE was espun onto the tube for 30 minutes under these conditions to yield an approximately 25μ (as deposited post sintering) thick covering of PTFE fibers.

After allowing the Biax tube/espun PTFE assembly to dry excess espun PTFE was removed and the composite graft was sintered on the SS tube for 10 minutes at 385° C. After cooling, isopropanol was used to facilitate the removal of the composite graft from the tube.

Example 2 Type I Construction: ePTFE/espun PTFE

Same as Example 1 except: After drying and removal of excess PTFE the tube assembly was then wrapped in 80μ stainless steel (SS) foil followed by being further wrapped with unsintered 25μ thick ePTFE membrane applied around the entire assembly. The tube assembly was then placed in an oven preheated to 385° C. for 15.0 minutes. Upon removal from the oven and cooling the SS foil and 25μ thick membrane were removed to reveal the composite graft. Isopropanol was used to facilitate the removal of the graft from the tube.

Example 3 Type II Construction: ePTFE/stent/espun PTFE

A biaxially (Biax) expanded approximately 6 cm long ePTFE tube with an intermodal distance (IND) of 20μ, internal diameter (ID) of 4 mm, wall thickness (WT) of 0.1 mm, and porosity of 77.27% was placed over and at the end of a 4 mm exterior diameter (OD) stainless steel tube of 35 cm length. A generic stent 5.2 cm long, 4.25 mm ID, and a WT of 0.125 mm was then expanded slightly, placed, and centered over the ePTFE tube. The ePTFE tube assembly was then positioned at the midpoint of the SS tube and placed into a rotating chuck such that it was positioned to allow espinning along the entire length of the turning tube assembly.

An approximately 85,900 cPs espinning dispersion based on a mixture of 4.2% (PEO/PTFE), 300,000 amu polyethylene oxide and Daikin D210 60% PTFE dispersion which had been allowed to homogenize and then turned and filtered to achieve a smooth consistency was placed into a 10 ml plastic syringe fitted with a 22 gauge needle. The syringe was placed into a Harvard Model 702100 syringe pump and set to a 2.0 ml/hour pumping rate. The needle tip was positioned at approximately 9.5 cm from the rotating stent/tube assembly. The rotation of the stent/tube assembly was approximately 60 rpm. A traverse was used to move the espinning needle along the length of the SS tube with a rate of travel of 3.2 mm/sec. The return points for the traverse were set at the ends of the Biax tube. A voltage of 9.2 kV was employed. PTFE was espun onto the tube for 60 minutes under these conditions to yield an approximately 50μ (as deposited post sintering) thick covering of PTFE fibers.

After allowing the tube assembly to dry the composite stent-graft was sintered on the SS tube for 15 minutes at 385° C. After cooling, isopropanol was used to facilitate the removal of the stent-graft from the tube.

Example 4 Type II Construction: ePTFE/stent/espun PTFE

Same as Example 3 except: After allowing the stent-tube assembly to dry it was then wrapped in 80μ stainless steel (SS) foil followed by being further wrapped with unsintered 25μ thick ePTFE membrane applied around the entire assembly. The stent-tube assembly was then placed in an oven preheated to 385° C. for 15.0 minutes. Upon cooling the SS foil and 25μ thick membrane were removed to reveal the stent-graft. Isopropanol was used to facilitate the removal of the graft from the tube.

Example 5 Type III Construction: ePTFE/espun PTFE/ePTFE

A biaxially (Biax) expanded approximately 10 cm long ePTFE tube with an intermodal distance (IND) of 20μ, internal diameter (ID) of 4 mm, wall thickness (WT) of 0.1 mm, and porosity of 77.27% was placed over and centered along a 4 mm exterior diameter (OD) stainless steel of 35 cm length. The tube assembly was placed into a rotating chuck such that it was positioned to allow espinning along the entire length of the turning tube assembly.

An approximately 85,900 cPs espinning dispersion based on a mixture of 4.2% (PEO/PTFE), 300,000 amu polyethylene oxide and Daikin D210 60% PTFE dispersion which had been allowed to homogenize and then turned and filtered to achieve a smooth consistency was placed into a 10 ml plastic syringe fitted with a 22 gauge needle. The syringe was placed into a Harvard Model 702100 syringe pump and set to a 2.0 ml/hour pumping rate. The needle tip was positioned at approximately 9.5 cm from the rotating tube assembly. The rotation of the tube assembly was approximately 60 rpm. A traverse was used to move the espinning needle along the length of the tube with a rate of travel of 3.2 mm/sec. The return points for the traverse were set at the ends of the Biax tube. A voltage of 9.2 kV was employed. PTFE was espun onto the tube for 60 minutes under these conditions to yield an approximately 50μ (as deposited post sintering) thick covering of PTFE fibers.

After allowing the tube assembly to dry at 50° C. for one hour an ePTFE membrane of basis weight 9.955 gsm and thickness of 28μ was wrapped 4 times around the tube assembly. The tube assembly was then wrapped with unsintered 25μ thick ePTFE membrane applied tightly around the entire assembly. The tube assembly was then placed into an oven preheated to 385° C. for 15.0 minutes. After cooling the 25μ thick membrane was removed to reveal the graft. Isopropanol was used to facilitate the removal of the graft from the tube.

Example 6 Type III Construction: ePTFE/espun PTFE/ePTFE

Same as Example 5 except: After allowing the tube assembly to dry an ePTFE membrane of basis weight 9,955 gsm and thickness of 28μ was wrapped 4 times around the tube assembly. The tube assembly was then wrapped in 80μ stainless steel (SS) foil followed by being further wrapped with unsintered 25μ thick ePTFE membrane applied around the entire assembly. The tube assembly was then placed in an oven preheated to 385° C. for 15.0 minutes. Upon cooling the SS foil and 25μ thick membrane were removed to reveal the graft. Isopropanol was used to facilitate the removal of the graft from the tube.

Example 7 Type IV Construction: ePTFE/stent/espun PTFE/ePTFE

A biaxially (Biax) expanded approximately 6 cm long ePTFE tube with an intermodal distance (IND) of 20μ, internal diameter (ID) of 4 mm, wall thickness (WT) of 0.1 mm, and porosity of 77.27% was placed over and at the end of a 4 mm exterior diameter (OD) stainless steel of 35 cm length. A generic stent 5.2 cm long, 4.25 mm ID, and a WT of 0.125 mm was then expanded slightly, placed, and centered over the ePTFE tube. The ePTFE tube assembly was then positioned at the midpoint of the SS tube and placed into a rotating chuck such that it was positioned to allow espinning along the entire length of the turning tube assembly.

An approximately 85,900 cPs espinning dispersion based on a mixture of 4.2% (PEO/PTFE), 300,000 amu polyethylene oxide and Daikin D210 60% PTFE dispersion which had been allowed to homogenize and then turned and filtered to achieve a smooth consistency was placed into a 10 ml plastic syringe fitted with a 22 gauge needle. The syringe was placed into a Harvard Model 702100 syringe pump and set to a 2.0 ml/hour pumping rate. The needle tip was positioned at approximately 9.5 cm from the rotating stent/tube assembly. The rotation of the stent/tube assembly was approximately 60 rpm. A traverse was used to move the espinning needle along the length of the rod with a rate of travel of 3.2 mm/sec. The return points for the traverse were set at the ends of the stent. A voltage of 9.2 kV was employed. PTFE was espun onto the tube for 60 minutes under these conditions to yield an approximately 50μ (as deposited post sintering) thick covering of PTFE fibers.

After allowing the tube assembly to dry an ePTFE membrane of basis weight 9.955 gsm and thickness of 28μ was wrapped 4 times around the stent/tube assembly. The stent/tube assembly was then wrapped with unsintered 25μ thick ePTFE membrane applied tightly around the entire assembly. The tube assembly was then placed into an oven preheated to 385° C. for 15.0 minutes. After cooling the 25μ thick membrane was removed to reveal the stent-graft. Isopropanol was used to facilitate the removal of the stent-graft from the tube.

Example 8 Type IV Construction: ePTFE/stent/espun PTFE/ePTFE

Same as Example 7 except: After allowing the tube assembly to dry an ePTFE membrane of basis weight 9.955 gsm and thickness of 28μ was wrapped 4 times around the stent-tube assembly. The stent-tube assembly was then wrapped in 80μ stainless steel (SS) foil followed by being further wrapped 5 times with unsintered 25μ thick ePTFE membrane applied around the entire assembly. The tube assembly was then placed in an oven preheated to 385° C. for 15.0 minutes. Upon cooling the SS foil and 25μ thick membrane were removed to reveal the stent-graft. Isopropanol was used to facilitate the removal of the graft from the tube.

In the interests of brevity and conciseness, any ranges of values set forth in this specification are to be construed as written description support for claims reciting any sub-ranges having endpoints which are whole number values within the specified range in question. By way of a hypothetical illustrative example, a disclosure in this specification of a range of 1-5 shall be considered to support claims to any of the following sub-ranges: 1-4; 1-3; 1-2; 2-5; 2-4; 2-3; 3-5; 3-4; and 4-5.

These and other modifications and variations to the present disclosure can be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present disclosure, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments can be interchanged both in-whole or in-part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the disclosure. 

What is claimed is:
 1. A composite structure comprising a tubular frame and comprising a first tubular polymeric layer defining an inner surface of the structure and a second tubular polymeric layer defining an outer surface of the structure, wherein at least one of the first tubular polymeric layer and second tubular polymeric layer comprises a plurality of polytetrafluoroethylene (PTFE) nanofibers.
 2. The composite structure of claim 1, wherein the composite structure is a stent and wherein at least one of the first tubular polymeric layer and tubular polymeric layer is configured to enhance cellular ingrowth.
 3. The composite structure of claim 2, wherein the plurality of PTFE fibers is a plurality of spun PTFE fibers.
 4. The composite structure of claim 2, wherein the plurality of spun PTFE fibers is a plurality of electrospun PTFE fibers.
 5. The composite structure of claim 2, further comprising a frame configured to exhibit radial strength and promote recovery during deployment of the stent.
 6. The composite structure of claim 2, wherein the plurality of PTFE fibers has a density such that there is a range of distances of about 0.1μ to about 50μ between points of contact of the fibers.
 7. The composite structure of claim 2, further comprising a third layer joined to the first layer and the second layer.
 8. The composite structure of claim 7, wherein the third layer is configured to inhibit cellular communication.
 9. The composite structure of claim 8, wherein both the first tubular polymeric layer and the second tubular polymeric layer are configured to enhance cellular ingrowth.
 10. The composite structure of claim 2, wherein one of the first tubular polymeric layer and the second tubular polymeric layer is configured to enhance cellular ingrowth into the respective layer and the other of the first tubular polymeric layer and the second tubular polymeric is configured to inhibit cellular ingrowth into the respective layer.
 11. The composite structure of claim 2, wherein the PTFE fibers are electrospun from a mixture comprising PTFE, polyethylene oxide, and water.
 12. A prosthetic device comprising a layer of nanofibers around a central lumen, wherein the nanofibers comprise polytetrafluoroethylene (PTFE).
 13. The prosthetic device of claim 12, comprising a tubular frame and a coating disposed on the tubular frame, the coating comprising the layer of PTFE nanofibers.
 14. The prosthetic device of claim 13, wherein the prosthetic device is a tubular vascular prosthesis comprising a luminal and abluminal surface, and the first layer of PTFE nanofibers is present on the luminal surface.
 15. The prosthetic device of claim 13, wherein the layer of PTFE nanofibers is a first layer of PTFE nanofibers, and the prosthetic device further comprises a second layer of PTFE nanofibers.
 16. The prosthetic device of claim 15, wherein the pore structure of one or more of the layers as defined by ASTM F316 is between about 0.05 μm and about 50 μm.
 17. The prosthetic device of claim 15, wherein one or more of the layers has a porosity to enhance cellular ingrowth or attachment.
 18. The prosthetic device of claim 15, wherein one or more of the layers has a porosity to inhibit cellular ingrowth or attachment.
 19. The prosthetic device of claim 13, wherein the layer of PTFE nanofibers has been spun from an aqueous dispersion comprising polytetrafluoroethylene.
 20. The prosthetic device of claim 13, wherein the layer of PTFE nanofibers comprises PTFE that has been spun onto a rotating assembly.
 21. The prosthetic device of claim 12, wherein the nanofibers comprise spun nanofibers in random orientation around the central lumen.
 22. The prosthetic device of claim 12, wherein the spun nanofibers comprise electrospun fibers.
 23. The prosthetic device of claim 12, further comprising a tubular frame.
 24. The prosthetic device of claim 12, wherein the prosthetic device is a graft.
 25. The prosthetic device of claim 12, wherein the layer of PTFE nanofibers is designed to enhance, inhibit, or retard the migration of endothelium.
 26. A method of constructing a prosthetic device, comprising: providing a frame; and applying a layer of polytetrafluoroethylene (PTFE) nanofibers to the frame to form a prosthetic device.
 27. The method of claim 26, further comprising applying a fluorinated ethlyene propylene (FEP) layer to the device.
 28. The method of claim 26, wherein the applying step comprises spinning PTFE onto a cylindrical frame and, thereafter, sintering the spun PTFE while in place on the frame. 